1. Field of the Invention
This invention relates to the formation of integrated circuit structures on semiconductor substrates. More particularly, this invention relates to the formation of a low dielectric constant carbon-containing silicon oxide dielectric material for integrated circuit structures.
2. Description of the Related Art
The shrinking of integrated circuits has resulted in levels of interconnects, including metal interconnects, being placed closer together, as well as reduction of the horizontal spacing between metal lines on any particular level of such interconnects. As a result, capacitance has increased between such conductive portions, resulting in loss of speed and increased cross-talk. One proposed approach to solving this problem of high capacitance is to replace the conventional silicon oxide (SiO2) dielectric material, having a dielectric constant (k) of about 4.0, with another insulation material having a lower dielectric constant to thereby lower the capacitance.
In an article by L. Peters, entitled xe2x80x9cPursuing the Perfect Low-K Dielectricxe2x80x9d, published in Semiconductor International, Volume 21, No. 10, September 1998, at pages 64-74, a number of such alternate dielectric materials are disclosed and discussed. Included in these dielectric materials is a description of a low k dielectric material having a dielectric constant of about 3.0 formed using a Flowfill chemical vapor deposition (CVD) process developed by Trikon Technologies of Newport, Gwent, U.K. The process is said to react methyl silane (CH3xe2x80x94SiH3) with hydrogen peroxide (H2O2) to form monosilicic acid which condenses on a cool wafer and is converted into an amorphous methyl-doped silicon oxide which is annealed at 400xc2x0 C. to remove moisture.
Carbon-containing silicon oxide insulating materials formed in this manner exhibit good gap-filling capabilities and at the same time are characterized by a dielectric constant less than 3.0 and remain stable during subsequent annealing at temperatures of up to 500xc2x0 C. However, to be able to deposit low k films characterized by these properties, as well as by good across-wafer and intra-wafer uniformities, the CVD process should be carried out under optimized conditions. Such optimized conditions have been found to be characterized by very narrow margins with regard to temperature, pressure, and flow rates.
In addition to thickness uniformity which sometimes varies in wide intervals, it has been found that during the formation of such low dielectric constant carbon-containing silicon oxide materials, unacceptably high carbon losses can occur during the reaction between the carbon-substituted silane and the hydrogen peroxide, i.e., carbon losses as high as 25 atomic %. It has also been found that during the reaction of the carbon-substituted silane and the hydrogen peroxide there are seemingly random spiking problems related to momentary pressure bursts. These variations can cause poor across-wafer thickness uniformity of the deposited film, as well as a xe2x80x9chazexe2x80x9d or condensation problem.
Sometimes the pressure spikes are high enough to actually stop the reaction by increasing the pressure in the reaction chamber sufficiently to interfere with the flow of reactants into the chamber. In any event, such pressure spiking and resultant rise in pressure can result in the precipitation of particles of the reaction product in the gas phase and their subsequent deposition on the substrate surface. This, in turn creates a mixture of flowable carbon-containing silicon oxide and solids, which can reduce the flowability of the material, resulting in an adverse effect on the step coverage of the material which can even result in the formation of voids between metal lines.
While this pressure spiking can be avoided by varying the CH3SiH3/H2O2 concentration ratio and/or total flows, the multi-factor character of such optimization makes it difficult to develop reliable technology by means of the process parameter variations only. Thus, the process has been found to be very sensitive to even small changes in temperature, pressure, and flow rates.
It would, therefore, be desirable to be able to make such low dielectric constant carbon-containing silicon oxide dielectric material by a process having decreased sensitivity to minor changes in temperature, pressure, and flow rates, while providing a product having uniform film thickness, a smooth surface, and low carbon loss.
The invention comprises an improvement in the formation of low dielectric constant carbon-containing silicon oxide dielectric material by reacting a carbon-substituted silane with a hydrogen peroxide oxidizing agent, wherein the process is carried out in the presence of a reaction retardant. The reaction retardant reduces the sensitivity of the reaction to changes in pressure, temperature, and flow rates, and results in the formation of a film of more uniform thickness across the substrate as well as a film with a smooth surface, with a low carbon loss during the reaction.
The reaction retardant is selected from the group consisting of:
1) an inorganic compound selected from the group consisting of: Cl2, Br2, I2, HF, HCl, HBr, HI, NO, NO2, N2O, H2S, CO, CO2, NH3, and SO2,
2) an organic compound selected from the group consisting of: a 1-6 carbon alkane, a 1-6 carbon alkene, a 1-6 carbon alkyne, a 1-6 carbon alcohol, a 1-6 carbon aldehyde, a 1-6 carbon ketone, a 1-6 carbon carboxylic acid, a 1-10 carbon aromatic, and any of the above organic compounds having one or more atoms therein selected from the group consisting of Cl, Br, I, S, N, and P; and
3) mixtures of any 2 or more of the above.